Hard carbon coatings such as diamond-like carbon (DLC) coatings are attractive coatings for example because of their high hardness and low coefficient of friction, their chemical inertness and their biocompatibility. One of the main problems of DLC coatings is the poor adhesion to a substrate.
It has been found that the application of one or more intermediate layers between the DLC coating and the substrate can promote the adhesion strength. A variety of interlayers have been tested, such as an interlayer of Ti, TiN or TiC.
FR 2 596 775 describes the use of a TiN—TiCN intermediate layer. However, adhesion of DLC coatings to the substrate is still an issue.